Check if a file is a text file in bash

Question

I am trying to make a check to see if the file being attached to the email is a text file, and if it is not it returns an error. However during testing, I provide a valid text.txt and it returns the "Invalid Attachment" message.

send_email()                
{
  message=
  address=
  attachment=
  validuser=1
echo "Enter the email address: "
read address
echo ""
getent passwd | grep -q $address
if [ "$?" = "0" ]
  then
    echo -n "Enter the subject of the message: "
    read message
    echo ""

    echo "Enter the file you want to attach: "
    read attachment
    attachmenttype='file $attachment | cut -d\  -f2'
    if [ $attachmenttype = "ASCII" ]
  then 
  mail -s "$message" "$address"<"$attachment"
  press_enter
elif [ $attachmenttype = "cannot" ]
  then 
  mail -s "$message" "$address"<"$attachment"
  press_enter
else
  echo "Invalid attachment"
  press_enter
fi
 else
    echo "Invalid username"
    press_enter
fi

}

Answer 1

Instead of

attachmenttype='file $attachment | cut -d\  -f2'

you should write :

attachmenttype=$(file "$attachment" | cut -d' ' -f2)

See http://wiki.bash-hackers.org/syntax/expansion/cmdsubst

---

or to get mime-type :

$ file -i "$attachmenttype" | cut -d' ' -f2
text/plain;

and decide what you want to do with the file depends of the type.